There were two parts to the study. The first part used 50 patients with CHF and 11 healthy controls. In these subjects, they recorded 10 min of spontaneous breathing and 4 min of breathing at the rates of 15, 6, and 3 breaths/min. They found that during spontaneous breathing, the resting SpO2 was lower in the CHF patients than in the controls. They also found that the SpO2 of the CHF patients was much less stable than that of controls. However, during the controlled breathing, SpO2 increased significantly and became more stable. At 3 breaths/min, the stability of the CHF patients was similar to that of the controls during spontaneous breathing.

Recordings also showed that, when compared to spontaneous breathing, the patients maintained a fairly consistent minute volume when breathing at 6 breaths/min, they increased their ventilation when breathing at 15 breaths/min, and they reduced their minute ventilation significantly at 3 breaths/min. Measurements revealed that breathing at both 6 and 3 breaths/min substantially improved ventilation-perfusion (the matching of air and blood flow in the lungs). Based on these findings, the authors concluded that breathing at 6 breaths/min might be the optimal rate to improve SpO2 without significant strain or difficulty.

The second portion of the study examined the impacts of consistent practice of slow breathing. They recruited 15 CHF patients (none that were in the first study) and had them learn slow breathing from a physiotherapist. They instructor emphasized reducing breathing rate and performing a “complete yoga breath,” breathing first into your belly, then the lower chest, and finally the upper chest, and then reversing the sequence for the expiration. They were advised to practice this breathing for 1 h a day for 1 month.

The patients reported that maintaining the slow breathing became easier with time and practice. And it paid off. The subjects showed a significantly lower spontaneous breathing rate and reported less signs of labored breathing after the study. Moreover, their SpO2 increased and they improved the amount of time they could exercise.

Overall, this study showed that slow breathing has both acute and long-term positive effects if practiced regularly. It has the immediate effects of increasing SpO2, increasing SpO2 stability, and increasing ventilation-perfusion in CHF patients. In long run, it has the benefits of improving SpO2, lowering spontaneous breathing rate, and improving exercise performance, all of which is directly applicable to diabetics who suffer from many of these same issues (e.g., lower resting SpO2). (In fact, the first author of this paper went on to study slow breathing in diabetes and performed a lot of great research, including publishing the 2017 Nature paper that concluded “Slow breathing could be a simple beneficial intervention in diabetes.”)

Abstract from Paper

BACKGROUND: In chronic heart failure (CHF), impaired pulmonary function can independently contribute to oxygen desaturation and reduced physical activity. We investigated the effect of breathing rate on oxygen saturation and other respiratory indices.

METHODS: Arterial oxygen saturation (SaO2) and respiratory indices were recorded during spontaneous breathing (baseline) and during controlled breathing at 15, six, and three breaths per min in 50 patients with CHF and in 11 healthy volunteers (controls). 15 patients with CHF were randomly allocated 1 month of respiratory training to decrease their respiratory rate to six breaths per min. Respiratory indices were recorded before training, at the end of training, and 1 month after training.

FINDINGS: During spontaneous breathing, mean SaO2 was lower in CHF patients than in controls (91-4% [SD 0.4] vs 95.4% [0.2], p<0.001). Controlled breathing increased SaO2 at all breathing rates in patients with CHF. Compared with baseline, minute ventilation increased at 15 breaths per min (+45.9% [9.8], p<0.01), did not change at six breaths per min, and decreased at three breaths per min (-40.3% [4.8], p<0.001). In the nine CHF patients who had 1 month of respiratory training, resting SaO2 increased from 92.5% (0.3) at baseline to 93.2% (0.4) (p<0.05), their breathing rate per min decreased from 13.4 (1.5) to 7.6 (1.9) (p<0.001), peak oxygen consumption increased from 1157 (83) to 1368 (110) L/min (p<0.05), exercise time increased from 583 (29) to 615 (23) min/s (p<0.05), and perception of dyspnoea reduced from a score of 19.0 (0.4) to 17.3 (0.9) on the Borg scale (p<0.05). There were no changes in the respiratory indices in the patients who did not have respiratory training.